1. Field of the Invention
The present invention is related to a matrix touch panel, and more particularly to a matrix touch panel balancing impedance variation caused by wire difference.
2. Description of the Related Art
Basic concept of matrix touch panels is similar to that of capacitive touch panel. Their difference lies in that transparent electrode layers of the matrix touch panels are etched and divided into a plurality of separated and juxtaposed transparent electrodes and the transparent electrodes on the upper panel and the transparent electrodes on the lower panel are perpendicularly intersected like rows and columns of a matrix. Each of the intersections of the transparent electrodes constitutes a capacitive switch generating variation of capacitance when touched. Such variation of capacitance can be further used to determine where coordinates of a touched intersection are located. Detailed structure of conventional matrix touch panels is disclosed further as follows:
With reference to FIG. 4, a matrix touch panel has a lower panel 70, an upper panel 80, an insulation layer 90 and a separation layer.
The lower panel 70 is made of glass. With reference to FIG. 5, the lower panel 70 is rectangular and has two long edges, two short edges, a transparent electrode layer, a plurality of wires 72 and a plurality of leading lines 73. The transparent electrode layer is etched and divided into a plurality of separated and juxtaposed first transparent electrodes 71 being parallel to the long edges and respectively having two ends. The wires 72 are divided into two sets and made of silver paste. The two sets of the wires 72 are symmetrically L-shaped and are formed on and alongside the two short edges respectively and one of the long edges simultaneously. The leading lines 73 are formed on a center portion of the long edge having the wires formed thereon and are formed by a plurality of electrical connection terminals. One terminal of each electrical connection terminal is connected with one terminal of the corresponding wire 72, and the other terminal of the wire 72 is connected to the corresponding end of the corresponding first transparent electrode 71. Hence, signals generated by the first transparent electrodes 71 can be sent out through the wires 72 and the leading lines 73.
The upper panel 80 structurally resembles the lower panel 70 except taking a form of a film. With reference to FIG. 6, the upper panel 80 is rectangular and has a bottom, two long edges, two short edges, a plurality of second transparent electrodes 81, a plurality of wires 82 and a plurality of leading lines 83. The second transparent electrodes 81 are separately and juxtaposedly formed on the bottom of the upper panel 80, are parallel to the short edges, respectively have two ends, and are perpendicularly overlapped on the first transparent electrodes 71 in the form of columns and rows of a matrix. The wires 82 are divided into two sets and made of silver paste. The two sets of the wires 82 are symmetrically U-shaped and are formed on and alongside one of the two long edges simultaneously, the two short edges respectively and the other of the two long edges simultaneously. The leading lines 83 are formed on a center portion of the long edge having the wires 82 formed thereon to correspond to the leading lines 73 and are formed by a plurality of electrical connection terminals. One terminal of each electrical connection terminal is connected with one terminal of the corresponding wire 82, and the other terminal of the wire 82 is connected to the corresponding end of the corresponding second transparent electrode 81. Hence, signals generated by the second transparent electrodes 81 can be sent out through the wires 82 and the leading lines 83.
The insulation layer 90 is frame-shaped, has a size matching that of the lower panel 70 and the upper panel 80, and is mounted between the upper panel 80 and the lower panel 70 to insulate the upper panel 80 from the lower panel 70.
The separation layer is formed by a plurality of spacers 91 located within the insulation layer 90 and distributed between the upper panel 80 and the lower panel 70 so as to form a gap between the upper panel 80 and the lower panel 70 before being touched.
The leading lines 73, 83 on the lower panel 70 and the upper panel 80 serve to connect with a flexible flat cable so that the touch panel is connected to a controller through the flexible flat cable. In other words, each transparent electrode 71 on the lower panel 70 and each transparent electrode 81 on the bottom of the upper panel 80 are connected with the external controller through the corresponding wires 72, 82, leading lines 73, 83 and the flexible flat cable. Based on the impedance-balancing concept, the leading lines 73, 83 are respectively located on center portions of the corresponding long edges of the lower panel 70 and the upper panel 80, ensuring that distances of the wires 72, 82 to the leading lines 73, 83 are roughly the same. Practically, the distances from the wires 72, 82 to the leading lines 73, 83 are hardly the same and there may be considerable differences among them. The reason is attributable to that original distances from the first and second transparent electrodes 71, 81 to the leading lines 73, 83 are already different. Hence, lengths of the wires 72, 82 in connection with the first and second transparent electrodes 71, 81 and the leading lines 73, 83 are also different. Given the lower panel 70 as an example, the first transparent electrodes 71 thereon are aligned transversely. The higher the first transparent electrode is located, the longer the distance between the first transparent electrode and the leading line 73. Such difference makes the wire 72 longer when the wire 72 is connected with the leading line 73 and the higher first transparent electrode 71, and shorter when the wire 72 is connected with the leading line 73 and the lower first transparent electrode 71. As the impedance value of the wire 72 is proportional to the length thereof, various wire impedance values exist between the first transparent electrodes 71 and the leading lines 73 and very likely result in erroneous determination of the location being touched.
Accordingly, to ensure the location-reading accuracy, the impedance variation of the wires should be tackled and further refined.